1. Field of the Invention
The present invention relates to a bent glass sheet shaping method and a bent glass sheet.
2. Description of the Related Art
As a method of bending-shaping a window glass, etc. of a vehicle, a bending-shaping method by press bending has been known.
The bending-shaping method by the press bending includes a method of curve shaping a glass sheet heated to a softening point by pressing the glass sheet with a press die having a curved surface to thereby curve the sheet, and a method of curving a softened glass sheet by sucking the glass sheet against a curved surface of a press die via a plurality of through holes provided in the press die with a vacuum device. A heat-resistant cover material is mounted onto the curved surface of the press die for preventing the softened glass sheet from being welded to the curved surface (for example, see Japanese Laid-open Patent Publication (Kokai) No. 2004-250257). 
On the other hand, a starting material glass sheet to be bending-shaped is produced by a float process (for example, see U.S. Pat. No. 3,700,542). The float process is to form a highly smooth glass sheet by pouring a molten glass onto molten tin.
However, the glass sheet formed by the float process has unevenness in component in a flowing direction of the molten glass, which may cause the glass sheet to be distorted in the flowing direction of the glass sheet.
In the bending-shaping method by the press bending, the cover material mounted onto the press die is made of knitted fabric of nonadhesive metal fiber, and produced while being wound into a roll. Alternatively, the cover material is knitted into a cylindrical shape, and produced into a flat shape by cutting a side surface of the cylinder. A difference in tension on the fiber or the like during the production causes the produced cover material to be waved substantially in the same direction, thereby providing waves on the cover material. When the glass sheet is pressed via the cover material having waves, the wave portions of the cover material are subjected to uneven heat, thereby causing portions of the glass sheet contacting the wave portions of the cover material to suffer thermal stress, which inevitably causes the produced bent glass sheet to be thermally distorted.
If a direction of the thermal distortions in the glass sheet caused by the waves in the cover material corresponds with a direction of distortions in the starting material glass sheet in the flowing direction of the molten glass, visibility distortions in the bent glass sheet significantly increases.
Using nonwoven fabric such as felt as the cover material can reduce the thermal distortions caused by the waves of the cover material, but the nonwoven fabric is less breathable, thereby disabling the glass sheet to be sucked via the plurality of through holes provided in the press die. Also, the nonwoven fabric is less stretchable, thereby making it difficult to cause the glass sheet to closely contact the press die, etc.